Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLUID FLOW CONTRO~ MEANS FOR PUMPS AND THE LIKE
Description
This invention relates to fluid machinery and, more
particularly, to a device designed to substantially retard
cavitation surging within such machinery.
As a skilled artisan may appreciate, fluid machines
such as pumps, which operate over a wide range of
capacities, are subjected to cavitation suxges at low flow
rates and at moderate to low values of Net Positive Suction
10 Head (NPSH). A flow rate of less than about 50~ of the
pump's design flow rate may be considered a low flow rate.
Moderate to low values of Net Positive Suction Head (NPSH)
are generally those that produce a pump pressure xise
reduction cf 1% to 3% below the pressure rise obtained in
the absence of NPSH influence.
When cavitation and recirculation exist
simultaneously, cavitation in the pump suction or intake
can, and often does, surge far upstream. Such surges often
create vibrations characterized by low frequency
20 shuttling. These vibrations, in turn, may cause numerous
mechanical problems, i.e., bearing failure, seal ~ailure,
and etc. As is evidenced ~rom the art, several attempts at
reducing pump cavitation have been made.
U. S. Patents 3!504,986; 4,375,937; and, 4,375,938
25 disc~ose various pump housings having fluidic passageways
provided therein for capturing recirculating fluids in a
manner reducing pump cavitation surge.
U. S. Patents 3,3~4,022; 3,664,759; 4,150,916; and,
4,239,453 disclose pumps having various restr~ction means
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disposed within the pump inlet passageway for redirecting
backflowing fluids in a manner reducing pump cavitation
surge.
This invention pertaine to a fluid machine having a
housing including a pumping chamber and conduit means
leading from the exterior of the fluid machine to the
pumping chamber. A rotodynamic means such as an impeller
may be provided within the pumping chamber for pumping
fluid by centrifugal force. If the pump means or impeller
is operated at flow rates much less less than optimum
efficiency point, a swirling fluid may eminate backflow
from the pumping chamber. This backflowing fluid usually
forms a fluid boundary layer about the fluid flowing toward
the pumping chamber.
The present invention is not intended to prevent the
pump from cavitating. Instead, the apparatus of the
present invention suppresses the cavitational surge in the
pump intake. With the present invention, operative means,
disposed upstream of the impeller and within the conduit
20 means, collects sufficient backflowing fluid and redirects
same into the inward flow whereby preventing cavitation
surging of the pump. Unlike other devices, the operative
means of the present invention requires minimal changes to
the pump housing. In contrast to some devices, the
25 operative means of the present invention includes an
` annulus assemblage having a plurality of radially inward
- extending stationary blades or vanes which are curved to
capture the swirling backflowing fluid. The vanes are
` designed, however, not to restrict or ~ubstantially
;` 30 interfere with the inward flowing fluid which is directed
toward the pumping chamber. As such, the fluid machine may
be operated at flow rates much les~ than optimum e~iciency
point without the noise and vibrational characteristic~
usually associated with such operation.
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In accordance with the above, a primary object of
this invention is to provide novel means which can be used
in combination with fluid machinery for retarding pump
cavitation surge whereby reducing an occurrence of noise
and vibration over a wide range of fluid flow rates.
Another object of this invention is the provision of
suitable means which can redirect a fluid counterflow
produced at the suction side of a fluid machine without
substantially interfering with ordinary fluid flow.
Another object of this invention is to provide novel
means adapted for use combination with fluid machinery for
retarding pump cavitation surge but which requires minimal
changes to the pump housing.
Yet another object of this invention is to provide
15 means for retarding pump cavitation surge which is simple
in construction and inexpensive.
Having in mind the above object and other attendant
advantages that would be evident from an understanding of
this disclosure, the invention comprises the devices,
combination and arrangement of parts as illustrated in the
presently preferred forms of the invention which are
hereinafter set forth in detail to enable those skilled in
the art to readily understand the function, operation,
construction and advantages of same when read in
conjunation with the accompanying drawing in which:
FIGURE l is a longitudinal sectional view of a fluid
' mac'nine incorporating in one embodiment of the present
`~ ir.vention;
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FIGURE 2 is an end view of another embodiment of the
present invention; and
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FIGURE 3 is a cross-sectional view taken along line
3-3 of FIGURE 2.
Turning now to the drawings, wherein like reference
numerals indicate like parts throughout the several views,
in FIGURE 1 there is illustrated a fluid machine 10 which
may be a centrifugal pump or the like. The fluid machine
10 includes a housing or casing 12 having a pumping chamber
14 and which is provided with conduit means 16 and 18
defining confined spaces through which fluid flows. In the
illustrated embodiment, conduit 16 acts as a fluid suction
intake or inlet passageway while conduit 18 acts as an
outlet passageway. Rotodynamic means 20 may be rotation-
ally arranged in the pumping chamber 14 in a manner creat-
ing fluid flow through said passageways. In the illustrated
embodiment, the rotodynamic means includes an impeller ~2
and may include an inducer 24 situated upstream from the
main impeller 22 and which operates in conjunction there-
with.
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As is Xnown in the art, the rotodynamic means 20 may
20 be operated over a range of flow rakes. When the
rotodynamic means is operated at flow rates much less than
optimum efficiency point, cavitation surging within the
fluid machine may occur. It is believed that cavitation
surging of the pump occurs when sufficient liquid hackflows
from khe pumping chamber. That is, there may be fluid
flow within the inlet passageway extending in two opposed
directions. one fluid flow is directed toward the pumping
chamber. The other fluid flow is that fluid backflowing
upstream ~rom the pumping chamber. The backflowing liquid
30 is caused at low flow rates since liquid cannot move
forward through the pump and, hence, backflows upstream.
The rotation of the impeller causes this liquid to swir}
upstream aisi it backflows. The swirling backflowing fluid
~ij tends to move outward toward the walls of the confined spaces by means of centrifugal force whereby forming a
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fluid boundary layer about the fluid flowing toward the
pumping chamber. To avoid cavitation surging, the swirling
and backflowing fluid must be straightened out and redi-
rected toward the center of the intake opening.
According to the present invention, a backflow
retardation device 30 is provided upstream of the impeller
22 and inducer 24 to suppress the cavitation surge.
Unlike other devices, the backflow preventer means 30 may
be arranged within the confined spaces of the housing
without significant changes to the inlet passageway 16.
From the depicted embodiment of the backflow retardation
device, in Figures 2 and 3, it may be seen to include an
annulus assembly comprised of a plurality of stationary
vanes 32 which radially extend transverse to the centerline
of the inlet opening. Each radial vane includes a blade
portion extending generally parallel to the inward direc-
tional fluid flow but which is also curved in design. The
curved design enables the blades 32 to act as a catching
means for collecting sufficient backflowing fluid and
redirecting same toward the center of the inlet
i passageway. This design allows for backflowing fluid to be
caught without interfering with the incoming flow to the
pump chamber and hence without interfering with pump
performance.
As apparent from the drawings, the vanes 32
terminate inwardly short of the center of said inlet
~;~ passageways. The innermost ends of the vanes 32 may be
secured to a hub 34 centrally disposed in the passageway
16. The outermost edges of the vanes 32 may be secured to
30 a ring 38 which acts as a securement means for the annulus
~ assembly.
;~ ~he backflow retardation device 30 according to the
invention is capable of collecting sufficient fluid
backflow from the impeller and redirecting same into the
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inlet stream to prevent cavitation surging of the pump. A
salient feature of the present invention is that it can
accomplish these ends without substantial changes or
reworking of the inlet passageway and more importantly the
5 pump housing. Moreover, the present invention effects
these desirous ends without adversely effecting the
incoming stream of fluid to the pump or th~ pumps per-
formance.
Thus, there has been provided a FLUID FLOW CONTROL
10 MEANS FOR PUMPS AND THE LIXE and which fully satisfies
objects, aims and advantages set forth above. While the
invention has been described in connection with specific
embodiment thereof, it is evident that many alternatives,
modifications and variations will be apparent to those
15 skilled in the art in light of the foregoing description.
Accordingly, it is intended to embrace all such
alternatives, modifications and variations as fall within
the spirit and broad s~ope of the appended claims which are
attached hereto and form a part hereof.
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